Recently, in the trend of higher speed and lower power consumption of semiconductor devices such as microcomputer and digital signal processor, the consumer electronic appliances are becoming higher and higher in performance, while extraneous emission such as the electromagnetic noise generated from these electronic appliances is posing serious problems. Accordingly, measures against extraneous emission are being demanded not only in electronic appliances but also in semiconductor devices used in them. The most effective measure against extraneous emission in semiconductor device is to install a capacitor of large capacity between the bias line and ground line, and hitherto a capacitor was connected outside of the semiconductor device.
On the other hand, lately, nonvolatile random access memory in simple constitution comprising a capacitor using a ferroelectric film, and dynamic random access memory using a capacitor made of dielectric film of high dielectric constant as a holding capacity are being developed.
A conventional semiconductor device having capacitor is specifically explained below. FIG. 1 is a partially sectional view of a representative semiconductor device. In FIG. 1, reference number 1 denotes a semiconductor substrate, and the integrated circuit formed on the semiconductor substrate 1 is omitted in the drawing. An insulating film 2 is formed on the semiconductor substrate 1. On the insulating film 2, metal interconnections 3, 4, 5 made of aluminum or aluminum alloy are formed. On these metal interconnections 3, 4, 5, an insulating film 6 is formed, and a bottom electrode 9, a ferroelectric film 10, and a top electrode 11 are formed on the insulating film 6, and the bottom electrode 9 is connected to the metal interconnection 4 through a contact hole 8, and the top electrode 10 to the metal interconnection 3 through a contact hole 7.
In FIG. 1, supposing the metal interconnection 3 to be bias line Vss and the metal interconnection 4 to be bias line Vdd, a capacitor comprising the bottom electrode 9, ferroelectric film 10 and top electrode 11 is inserted between the bias line Vss and bias line Vdd.
A manufacturing method of the conventional semiconductor device having capacitor shown in FIG. 1 is described below. On the insulating film 2 on the semiconductor substrate 1 on which integrated circuits and others are formed, a metal film of aluminum or aluminum alloy is formed by sputtering or other method. This metal film is etched by ordinary photoetching method, and the metal interconnections 3, 4, 5 are formed. Consequently, on the entire surface of the semiconductor substrate 1, the insulating film 6 is formed by CVD method, and the contact holes 7,8 are formed in specified areas of the insulating film 6 by photoetching method. A metal film is then formed on the insulating film 6, and this metal film is photoetched to form the bottom electrode 9. Including the upper part of the bottom electrode 9, the ferroelectric film 10 is formed by sputtering. After removing the ferroelectric film 10 in the contact hole 7, an aluminum film or aluminum alloy film is formed, and the top electrode 11 is formed by photoetching.
In such conventional semiconductor device having capacitor, however, since the ferroelectric film 10 is formed in the contact state of the bottom electrode 9 with the metal interconnection 4 of the integrated circuit, it is required that the material of the bottom electrode 9 should not react with the metal interconnection 4 at the time of heat treatment of the ferroelectric film 10, and that the insulating film 6 and the ferroelectric film 10 should adhere firmly to each other. It is, actually, difficult to select the material that satisfies these conditions. For example, when aluminum is used for the metal interconnections 3, 4, 5, and aluminum is also used for the bottom electrode 9, matching is excellent in their mutual relation and adhesion with the insulating film 6, but when oxide ferroelectric material such as BaTiO.sub.3 and PZT is used as the ferroelectric film 10, aluminum and the ferroelectric film 10 react with each other, which causes to vary the capacity of the capacitor.
Besides, in such conventional semiconductor device having capacitor, the metal interconnections 3, 4, 5 have been already formed when forming the ferroelectric film 10, and a part of the metal interconnections 3, 4, 5 is contacting with the diffusion layer (not shown in FIG. 1) of the semiconductor substrate 1, and therefore the ferroelectric film 10 cannot be treated at high temperature. That is, when the metal interconnections 3, 4, 5 are aluminum and the semiconductor substrate 1 is a silicon substrate, when heated at 450.degree. C. or higher, aluminum may invade into the diffusion layer in spikes to penetrate through the diffusion layer.
In the conventional semiconductor device having capacitor, moreover, after forming the contact holes 7 and 8 simultaneously on the insulating film 6, the bottom electrode 9 is formed, and then ferroelectric film 10 is formed thereon. Therefore, at the time of heat treatment of ferroelectric film 10, the reaction product due to reaction between ferroelectric film 10 and metal interconnection 3 is formed in the bottom of the contact hole 7. This reaction product is left over also when removing the ferroelectric film 10, which may cause contact failure between the metal interconnection 3 and top electrode 11.
On the other hand, in the method of first forming the contact hole 8 then forming the contact hole 7 after forming the ferroelectric film 10, both ferroelectric film 10 and insulating film 6 must be etched, but the etchant satisfying the both etching conditions differs, and the process is complicated.